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<TITLE>MatSeqSBAIJSetPreallocation</TITLE>
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<div id="version" align=right><b>petsc-3.7.5 2017-01-01</b></div>
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<A NAME="MatSeqSBAIJSetPreallocation"><H1>MatSeqSBAIJSetPreallocation</H1></A>
Creates a sparse symmetric matrix in block AIJ (block compressed row) format. For good matrix assembly performance the user should preallocate the matrix storage by setting the parameter nz (or the array nnz). By setting these parameters accurately, performance during matrix assembly can be increased by more than a factor of 50.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscmat.h"
PetscErrorCode MatSeqSBAIJSetPreallocation(Mat B,PetscInt bs,PetscInt nz,const PetscInt nnz[])
</PRE>
Collective on <A HREF="../Mat/Mat.html#Mat">Mat</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>B </B></TD><TD>- the symmetric matrix
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>bs </B></TD><TD>- size of block, the blocks are ALWAYS square. One can use <A HREF="../Mat/MatSetBlockSizes.html#MatSetBlockSizes">MatSetBlockSizes</A>() to set a different row and column blocksize but the row
blocksize always defines the size of the blocks. The column blocksize sets the blocksize of the vectors obtained with <A HREF="../Mat/MatCreateVecs.html#MatCreateVecs">MatCreateVecs</A>()
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>nz </B></TD><TD>- number of block nonzeros per block row (same for all rows)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>nnz </B></TD><TD>- array containing the number of block nonzeros in the upper triangular plus
diagonal portion of each block (possibly different for each block row) or NULL
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<DT><B>-mat_no_unroll </B> -uses code that does not unroll the loops in the
block calculations (much slower)
<br>
<DT><B>-mat_block_size </B> -size of the blocks to use (only works if a negative bs is passed in
<br>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
Specify the preallocated storage with either nz or nnz (not both).
Set nz=<A HREF="../Sys/PETSC_DEFAULT.html#PETSC_DEFAULT">PETSC_DEFAULT</A> and nnz=NULL for PETSc to control dynamic memory
allocation. See Users-Manual: ch_mat for details.
<P>
You can call <A HREF="../Mat/MatGetInfo.html#MatGetInfo">MatGetInfo</A>() to get information on how effective the preallocation was;
for example the fields mallocs,nz_allocated,nz_used,nz_unneeded;
You can also run with the option -info and look for messages with the string
malloc in them to see if additional memory allocation was needed.
<P>
If the nnz parameter is given then the nz parameter is ignored
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Mat/MatCreate.html#MatCreate">MatCreate</A>(), <A HREF="../Mat/MatCreateSeqAIJ.html#MatCreateSeqAIJ">MatCreateSeqAIJ</A>(), <A HREF="../Mat/MatSetValues.html#MatSetValues">MatSetValues</A>(), <A HREF="../Mat/MatCreateSBAIJ.html#MatCreateSBAIJ">MatCreateSBAIJ</A>()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/mat/impls/sbaij/seq/sbaij.c.html#MatSeqSBAIJSetPreallocation">src/mat/impls/sbaij/seq/sbaij.c</A>
<BR><A HREF="./index.html">Index of all Mat routines</A>
<BR><A HREF="../../index.html">Table of Contents for all manual pages</A>
<BR><A HREF="../singleindex.html">Index of all manual pages</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/mat/examples/tutorials/ex17.c.html">src/mat/examples/tutorials/ex17.c.html</A><BR>
<A HREF="../../../src/ksp/ksp/examples/tutorials/ex2.c.html">src/ksp/ksp/examples/tutorials/ex2.c.html</A><BR>
<A HREF="../../../src/snes/examples/tutorials/ex48.c.html">src/snes/examples/tutorials/ex48.c.html</A><BR>
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